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New research shows that intensive hunting of male capercaillies altered their DNA genetic sequence and decimated the population

September 22, 2015

New research published in ‘Conservation Genetics', in which the University of Oviedo takes part, provides new information about the decrease in the population of this type of birds in the Cantabrian Mountains

Intensive and selective hunting of male capercaillies in the Cantabrian Mountains until the middle of the 20th century may have caused the decrease in the population of this species, which is nowadays endangered. This is the working hypothesis of an international team which is joined by the Biodiversity Mixed Research Unit of the University of Oviedo. The resulting conclusions have been published in the journal Conservation Genetics.

The Cantabrian capercaillie, known by its scientific name as Tetrao urogallus cantabricus, is a subspecies of the western capercaillie. The reasons for the decrease in their population were not clear at all. The study emphasizes the possible consequences of hunting male specimens, dominant males, in the courting season, to be subsequently shown as trophies.

Scientists have analyzed the genetic information collected from Cantabrian specimens, hunted and stuffed, in the western area of the Cantabrian Mountains since 1958

To reach this conclusion researchers have analyzed the genetic information obtained from Cantabrian capercaillies hunted or stuffed, in the western area of the Cantabrian Mountains since 1958, as well as the feathers collected in the landscape of the same geographic area until 2007.

"Each time a capercaillie is hunted its genes are taken away from that population, especially if that specimen has not had the possibility of reproduction yet", according to explanation of María José Bañuelos, member of the Biodiversity Mixed Research Unit of the University of Oviedo and co-author of the publication. "Animals were killed when they were in the middle of the courtship process, moment in which dominant males performed special displays and sang to attract female counterparts, she added". This was actually the worst moment. The best specimens, those that could ensure generational replacement, were systematically killed. Males were attractive targets due to their bright plumage. Females, with a smaller body size, had an enigmatic behavior, which made them less attractive for hunters.

The team in charge of this work believed that it was actually the excessive hunting of male specimens, banned in 1979, what caused the demographic decline. The genetic information that experts analyzed suggests researchers were right.

Bañuelos states that the information analyzed shows that killing dominant males, on a permanent basis, resulted in something more than a simple numerical loss of specimens. "According to our information –she says—there is a sudden decrease of the genetic variability of males coinciding with more intensive legal hunting, which may be understood as a decline in the quantity and/or quality of males." This is actually what researchers call a genetic bottleneck.

The results go even further and indicate that killing males could have caused a general decline, affecting females as well. Therefore, several years after the prohibition, there is another sudden decline, another bottleneck, this time affecting females. "We believe that this second bottleneck could have been caused by a decrease in the reproduction process of females, due to the limited quantity and maybe quality of available males", says researcher of the University of Oviedo.

The research team, which includes experts from the University of Exeter and the Museum of Natural Sciences of Argentina, came to these conclusions after comparing samples of nuclear and mitochondrial DNA. Bañuelos explains the differences. Part of the DNA is only inherited from the mother, and that is mitochondrial DNA. Another part is inherited from both parents, nuclear DNA. Thus, comparing both types of DNA over time, we may rebuild the background of male and females "We have found evidence that, coinciding with the most intensive hunting period, mitochondrial DNA remained stable while nuclear DNA suffered a noticeable decrease in the genetic variability". In other words, while the population of females did not suffer any changes, there was a strong decrease in the quantity and quality of breeding males.

It is curious that, ten years later, when hunting was already banned, there was a reduction of mitochondrial DNA and quality of reproductive females. "We believe that this effect could be related to a worse reproductive capacity of females due to the limited available males", explains Bañuelos. And she added that: "It is possible that, due to decades of intensive hunting and subsequent years, few females were able to be fertilized and/or they actually copulated with subordinate males, as dominant males were frequently being hunted". In the medium term, this could have led to worse results in reproduction processes and a general decline in population. The collected data "are relevant not only to explain what happened to capercaillies, but also to highlight the effect that hunting may have on some populations", states the researcher.

Is the prohibition of hunting encouraging? María José Bañuelos explains that the study reveals –and it is actually one of its most remarkable results—that the effects of indiscriminate hunting have remained over time and have affected both males and females. "However, capercaillies still exist, and they have been reproducing since then, so in that sense there is still hope", remarks researcher of the University of Oviedo. "It is important to know which demographic parameters –gender, survival rate in adult specimens, reproduction rate—would be advisable to deal with in order to improve and increase their population", she says.